Heat developer

ABSTRACT

Apparatus for uniformly developing a light-exposed sheet of radiation-sensitive heat-developable film on a heating platen which assures uniform film contact with the heated surface and uniform heat transfer and development. The developer has a pivotably mounted transfer platen which initially receives the exposed sheet material and retains it thereon by use of an air pump. A valve mechanism controls the air pressure to the transfer platen and is operated to subsequently position the sheet material on a heating platen.

United States Patent Inventors Richard Alan Devries New Brighton; David C. Dornberg, Mahtomedi, both of Minn. Appl. No. 852,230 Filed Aug. 22, 1969 Patented Sept. 28, 1971 Assignee Minnesota Mining and Manufacturing Company St. Paul, Minn.

HEAT DEVELOPER 1 Claim, 2 Drawing Figs.

0.8. CI. .Q 95/89 R, 34/ 148 Int. Cl G03d 13/00 Field of Search 95/89, 89 G, 94 G; 355/87, 91; 34/148, 155

[56] References Cited UNITED STATES PATENTS 2,228,562 1/1941 Dieterle 95/89 UX 3,306,176 2/1967 Myers 355/91 3,440,944 4/1969 Endermann et al 95/89 3,455,634 7/1969 Guffon 355/91 3,478,665 11/1969 Umahashi et al. 95/89 Primary Examiner-Samuel S. Matthews Assistant Examiner-Fred L. Braun Attorney-Kinney, Alexander, Sell, Steldt & Delahunt I s H. /3/ 1.

HEAT DEVELOPER This invention relates to a platen type film processor and more specifically to a device capable of unifonn development of visible images in light-exposed radiation-sensitive heatdevelopable sheet materials.

A type of radiation-sensitive thermally developable sheet material which is particularly useful for making a visible record of a light image has a sensitive coating comprising a combination of photosensitive silver halide and light-stable organic silver salt in conjunction with a reducing agent, as described for example in U.S. Pat. No. 3,457,075. Thermal development to a uniform end-point requires consistent heat transfer throughout the entire sheet of light-exposed material to be developed, which requires that the entire sheet be in intimate contact with the heating platen. As both the time of exposure to, and temperature of, the heat source is critical, the initial contact must be uniform throughout the sheet, with no adjustment of the sheet being permitted after exposure to the heat source.

With prior art platen-type heating devices, it is difficult to introduce the exposed sheet material to the heat source without producing wrinkles or curls in the sheet material. These wrinkles or curls cause formation of a nonuniform developed image due to nonuniform heat transfer. lt has now been found possible to introduce the heatdevelopable sheet material uniformly to the heated platen and thus assure uniform development throughout the sheet by means of an inexpensive, low-maintenance apparatus now to be described in conjunction with the appended schematic drawing, in which:

FIG. 1 is a view of a preferred form of the apparatus in perspective, and

FlG. 2 is a sectional and partially schematic elevation taken approximately at line 2-2 of HO. 1.

The apparatus as illustrated in FIG. 1 comprises a cabinet 31, a bottom processor heater 32, a top transfer platen 33, and processing controls including a fan switch 26, a heater switch 25 and an adjustable automatic timer 27.

The top transfer platen 33 is hingedly attached to the top of the cabinet 31 on hinges 29 and consists of a hollow cover 12 having a flat porous sheet-retaining bottom member 11, forming a plenum chamber 13. Adjustable spacers 35 are provided along at least two opposite edges of the platen 33. The chamber 13 has an opening 14 through which it is connected to a valve assembly 28 by means of a flexible connecting tube 16. The valve assembly 28 is connected in turn to the inlet and outlet of an air pump such as a fan 15.

The bottom processor heater 32 consists of a hollow base 18 having a porous heat conductive top heating member 17, forming a plenum chamber 19. Chamber 19 has an opening 20 through which it is connected to the valve assembly 28 by means of a connecting tube 21. A heat source 22 supplies heat to heating member 17, and is regulated by a temperature controller 24 in conjunction with a temperature-sensing element '23. This maintains the preselected temperature of the heating member 17, which is set by means of a rheostat 30. The heat source 22 is activated, through suitable circuitry, not shown,

by turning on switch 25. Electrical power is supplied through a connecting cord and plug 34.

The fan 15 is activated by turning on switch 26 and an adjustable timer 27 controls automatically the timing of the several operations necessary to develop a sheet of film.

Following is a description of the functional operation of the apparatus. Valve 28 is initially in position to connect the chamber 13 with the inlet and the chamber 19 with the outlet respectively of the fan 15. The heater 22 is activated by turning on switch to bring the heating member 17 to the preset temperature. A sheet of light-exposed, heat-developable film is placed against the unheated retaining member 11, positioned accurately, and held in place while the fan 15 is activated by turning on switch 26. The resulting negative pressure in chamber 13 causes the developable sheet of film to be held against retainin member 11.

The top transfer p aten 33 is now pivoted against the heating member 17, the spacers 35 contacting the corresponding edges of member 17. The automatic timer 27, which has been set according to the requirements of the particular sheet material, is activated by the operator, causing valve 28 to reverse its position, creating a positive pressure at the surface of retaining member 11 and a negative pressure at the surface of heating member 17. The sheet material is thus forced off the top transfer platen 33 and onto the bottom processor heater 32. The sheet material is smoothly transferred without wrinkling and makes uniform smooth contact with the heating member 17. The operator may then pivot the top transfer platen 33 away from the bottom processor heater 32 so as to be able to observe the completion of the developing step under appropriate safe light.

As soon as the film has been fully developed, the automatic timer 27 again reverses the position of valve 28 creating a positive pressure at the surface of the heating member 17, and causing the developed film to float on a cushion of air above said member. The film is lifted away, and the switch 26 is turned off. The processor is then in readiness for another cycle.

In an illustrative embodiment useful in processing the heatdevelopable sheet material referred to hereinbefore, the plate 17 has an effective area of 10Xl3 inches, is one-fourth inch thick and is made of sintered and compressed bronze powder. Such a plate is available as a porous filter plate useful in filtering IO-micron particles and permitting the passage of one-half cubic foot of air per minute per square inch at room temperature and under a pressure drop of 8 inches of water. The plate is heated by a thermofoil electrical resistance heater element sandwiched between glass-cloth-reinforced silicone rubber films and bonded to the lower plate surface in a uniform pattern by vulcanization under heat and pressure. The element covers approximately 60-70 percent of the plate area. A glass bead thermistor temperature-sensing element is mounted within a suitable opening in the porous plate.

The upper plate 11 may for convenience be a duplicate of the plate 17, but may alternatively and more economically be a thinner plate of the same sintered bronze structure, e.g. of about one-eighth inch thickness, or a flat metal plate of onesixteenth inch thickness uniformly perforated with 0.06-inch holes on linch centers. -inch With the plate 17 as above described, the fan 15 maintains a negative pressure of 8 inches of water in the plenum chamber 19. With a 9X11 inch sheet of film over the plate surface, the vacuum increases to 14 inches of water. These values are sufficient to maintain the sheet in smooth uniform contact with the surface of either of platens 11 and 17 and to ensure rapid transfer of the sheet from platen 11 to platen 17.

What is claimed is as follows:

1. Apparatus for uniformly heat developing a light-exposed heat-developable sheet material and comprising, in combination: a cabinet; a hollow base, supported by said cabinet, and having a porous, flat, film-supporting, heat-conductive top platen member and including heating means for uniformly heating said top member; a hollow cover hingedly connected to said cabinet and having a porous flat film-supporting bottom retaining platen member; air pump means contained within said cabinet for providing both positive and negative air pressure; valve means connected between said air pump and said base and cover for directing positive air pressure to one of said base and cover while directing negative air pressure to the other; and switching means for reversing said valve means. 

1. Apparatus for uniformly heat developing a light-exposed heatdevelopable sheet material and comprising, in combination: a cabinet; a hollow base, supported by said cabinet, and having a porous, flat, film-supporting, heat-conductive top platen member and including heating means for uniformly heating said top member; a hollow cover hingedly connected to said cabinet and having a porous flat film-supporting bottom retaining platen member; air pump means contained within said cabinet for providing both positive and negative air pressure; valve means connected between said air pump and said base and cover for directing positive air pressure to one of said base and cover while directing negative air pressure to the other; and switching means for reversing said valve means. 